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Vitamin B12 - QuickFacts

Posted Sep 29 2010 2:26pm

Office of Dietary Supplements • National Institutes of Health

What is vitamin B12 and what does it do?

Vitamin B12 is a nutrient that helps keep the body’s nerve and blood cells healthy. It also helps prevent a type of anemia that makes people tired and weak.

How much vitamin B12 do I need?

It depends on your age. Here are the amounts people of different ages should get on average each day in micrograms (mcg):

Birth to 6 months 0.4 mcg
Infants 7-12 months 0.5 mcg
Children 1–3 years 0.9 mcg
Children 4–8 years 1.2 mcg
Children 9–13 years 1.8 mcg
Teens 14-18 years 2.4 mcg
Adults 2.4 mcg
Pregnant teens and women 2.6 mcg
Breastfeeding teens and women 2.8 mcg

What foods provide vitamin B12?

Foods from animals, but not plants, naturally have vitamin B12. You can get enough vitamin B12 by eating a variety of foods including beef liver, clams, fish, meat, poultry, eggs, milk, and other dairy products. Vitamin B12 is added to some breakfast cereals and other food products (check the product labels).

What kinds of vitamin B12 dietary supplements are available?

Almost all multivitamins have vitamin B12. Some dietary supplements have vitamin B12 only. Others have vitamin B12 with folic acid, vitamin B6, and other nutrients.

You can also get vitamin B12 from a shot or a nasal gel with a doctor’s prescription. These forms are usually used to treat vitamin B12 deficiency.

Am I getting enough vitamin B12?

Most people get enough vitamin B12 from the foods they eat. But some people have trouble absorbing vitamin B12 and might have a deficiency, even if they get enough vitamin B12.

Many older adults, for example, have trouble absorbing the vitamin B12 found naturally in food. However, most older adults can absorb the vitamin B12 that is added to fortified foods, such as some breakfast cereals, and dietary supplements. People over age 50 should get most of their vitamin B12 from these sources.

People with pernicious anemia have trouble absorbing vitamin B12 from all foods and dietary supplements. Others who might have trouble getting enough vitamin B12 include people who eat little or no animal foods such as strict vegetarians and vegans; people who have had weight loss surgery; and people with digestive disorders, such as celiac disease or Crohn’s disease. Your doctor can test your vitamin B12 level to see if you have a deficiency.

What happens if I don’t get enough vitamin B12?

People who don’t get enough vitamin B12 can have many symptoms. Some of these are tiredness, weakness, memory loss, constipation, loss of appetite, weight loss, and anemia. Nerve problems such as numbness and tingling in the hands and feet can also occur.

What are some effects of vitamin B12 on health?

Scientists are studying vitamin B12 to see how it affects health. Here are a few examples of what this research has shown:

Heart disease

Research on vitamin B12, usually combined with folic acid and vitamin B6, shows that taking vitamin B12 does not reduce the risk of having a heart attack or stroke.


As they get older, some people develop dementia or confusion. Scientists don’t know yet whether vitamin B12 helps prevent or treat dementia.

Energy and athletic performance

Vitamin B12 supplements do not appear to improve energy or athletic performance, except in people with a vitamin B12 deficiency.

Can vitamin B12 be harmful?

Vitamin B12 has not been shown to cause any harm.

Are there any interactions with vitamin B12 that I should know about?

Yes. For example, metformin for diabetes as well as some medicines that people take for acid reflux and peptic ulcer disease can affect how well the body absorbs vitamin B12.

Bottom line: Tell your doctor, pharmacist, and other health care providers about any dietary supplements and medicines you take. They can tell you if those dietary supplements might interact or interfere with your prescription or over-the-counter medicines or if the medicines might affect how your body uses vitamin B12.

Where can I find out more about vitamin B12?

Office of Dietary Supplements Health Professional Fact Sheet on Vitamin B12

Office of Dietary Supplements Consumer Fact Sheet on Vitamin B12

Vitamin B12 content of selected foods

For advice on buying dietary supplements, see the Office of Dietary Supplements Frequently Asked Questions

For information on the government’s food guidance systems, see MyPyramid and the Dietary Guidelines for Americans


This fact sheet by the Office of Dietary Supplements provides information that should not take
the place of medical advice. We encourage you to talk to your healthcare providers (doctor,
registered dietitian, pharmacist, etc.) about your interest in, questions about, or use of dietary supplements and what may be best for your overall health.

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